GB1476202A - Three-phase x-ray apparatus - Google Patents

Abstract

1476202 Supply systems for X-ray apparatus PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 16 July 1974 [19 July 1973] 31428/74 Heading H2H X-ray apparatus including an X-ray tube 1 comprises a three phase autotransformer 6 arranged to supply the tube 1 by way of a conventional transformer-rectifier unit 2 with an unsmoothed unidirectional high voltage, the cathode heater of the tube and the three phase transformer being fed from alternating supplies of the same frequency, the cathode of the tube having a low thermal inertia such that a significant fluctuation occurs in the cathode temperature and therefore in the emission current at twice the supply frequency, causing a ripple component to be present in the high voltage applied to the X-ray tube 1, an electrical asymmetry being introduced into the three phase input to the unit 2 such that the rectified high voltage applied to the tube contains a further ripple component at twice the supply frequency which further ripple has amplitude and phase adjustments associated therewith so as to reduce or compensate the first mentioned ripple. The three phase asymmetry may be produced by differing adjustments on the series connected variable resistors 7a, 7b, 7c, by asymmetrically adjusting the tappings on the autotransformer 3 or by varying the phase transformation ratios of the transformer in the unit 2. Yet again resistors 4a, 4b, 4c, shortcircuitable by means of contacts 5a, 5b, 5c respectively, may be asymmetrically arranged. Contacts 3a, 3b, 3c are closed by a timing mechanism during exposure.